Optically scanning displacement sensor with linearity correction means

Abstract

An optically scanning displacement sensor is arranged to compute by means of a triangulation an inverse function from a first measured distance signal proportional to output position signals from a position detecting means which receiving reflected light from an object to be detected, and the first measured distance signal is multiplied at a linearity correcting means by a signal of a sum of the inverse function and a constant so as to compute a second measured distance signal, whereby a two-dimensional position detection can be realized with the least required memory capacity and the minimum adjusting process.

What we claim as our invention is: 
     
       1. An optically scanning displacement sensor by means of a triangulation, the sensor comprising a light projecting means for radiating a light beam, a deviating means for deviating said light beam from said light projecting means towards an object to be detected and scanning said object, a light receiving optical means for condensing reflected light of said beam from said object and allowing said condensed reflected light to pass through said optical means, a position detecting means generating a pair of output position signals of values opposite to each other in response to a position on said position detecting means of a spot of said condensed light from said optical means, an operational means for operating on the basis of said pair of output position signals a distance of said object to generate a measured distance signal by adding and subtracting the pair of output position signals to operate a ratio between the position signals, and a linearity correcting means with respect to said measured distance, which correcting means obtaining a first distance signal proportional to said output position signals from said position detecting means to compute an inverse function and multiplying said first distance signal by a signal of a sum of said inverse function and a constant to compute a second distance signal proportional to a displacement of said distance of said object. 
     
     
       2. A sensor according to claim 1 wherein a first correction value to be added to said first distance signal, a second correction value to be added to said inverse function and a third correction value to be added to said constant are set for every scanning angle of said deviating means. 
     
     
       3. An optically scanning displacement sensor by means of a triangulation, the sensor comprising a light projecting means for radiating a light beam, a deviating means for deviating said light beam from said light projecting means towards an object to be detected and scanning said object, a light receiving optical means for condensing reflected light of said beam from said object and allowing said condensed reflected light to pass through said optical means, a position detecting means generating a pair of output position signals of values opposite to each other in response to a position on said position detecting means of a spot of said condensed light from said optical means, an operational means for operating on the basis of said pair of output position signals a distance of said object to generate a measured distance signal by adding and subtracting the pair of output position signals to operate a ratio between the position signals, and a linearity correcting means for correcting any non-linearity of said measured distance signal, wherein said light receiving optical means comprises an anamorphic optical means set to retain a swinging width of said condensed light spot on light receiving surface of said position detecting means following said scanning by said light beam over said object to be detected substantially to be within a width of said position detecting means. 
     
     
       4. A sensor according to claim 3 wherein said anamorphic optical means comprises a system of a convex lens, a cylindrical concave lens and a cylindrical convex lens. 
     
     
       5. A sensor according to claim 1 wherein said sensor is provided for use in a welding of working members which forming said object, and said operational means carries out an operation of determining a value of stepped part in said working members, said welding being made with respect to said stepped part, and computing a gap value between the working members by subtracting a thickness value of the respective members from said stepped part value. 
     
     
       6. A sensor according to claim 1 wherein said linearity correcting means comprises a high speed operational processor. 
     
     
       7. An optically scanning displacement sensor by means of a triangulation, the sensor comprising a casing having light projecting and receiving apertures, means provided in said casing for projecting a light beam, means provided in said casing for deviating said light beam from said light projecting aperture towards an object to be detected, a light receiving optical means disposed inside said light receiving aperture of said casing for condensing reflected light from said object, a position detecting means disposed to receive said condensed light for generating a pair of output signals of values opposite to each other in response to a position on said position detecting means of a spot of said condensed light from said optical means, an operational means for operating on the basis of said pair of output position signals a distance of said object to generate a measured distance signal by adding and subtracting the pair of output position signals to operate a ratio between the position signals, a linearity correcting means for correcting non-linearity of said measured distance signal, a protective cover of an optical plastic material and provided to each of said light projecting and receiving apertures of said casing, and a frame member for dismountably securing each of said protective covers to front face at each of said apertures of the casing. 
     
     
       8. A sensor according to claim 7 wherein said casing is further provided with permanent magnets disposed adjacent said light projecting and receiving apertures, and said frame members are formed by a ferromagnetic material to be magnetically coupled to said permanent magnets, for said dismountable securing of said protective covers.